1. Field of the Invention
The present invention relates to a bidirectional shift register, and more specifically, to a bidirectional shift register having transistors of a same type.
2. Description of the Prior Art
Please refer to FIG. 1, which is a circuit diagram of a complementary metal oxide semiconductor (CMOS) bidirectional shift register 10 made by applying low temperature poly silicon (LTPS) technology on a glass substrate according to the prior art.
The bidirectional shift register 10 comprises a former stage SR latch circuit 12, a former stage bidirectional control circuit 14 corresponding to the former stage SR latch circuit 12, a latter stage SR latch circuit 16, and a latter stage bidirectional control circuit 18 corresponding to the latter stage SR latch circuit 16. The former stage control circuit 14 is coupled between the former stage SR latch circuit 12 and the latter stage SR latch circuit 16. The latter stage bidirectional control circuit 18 is coupled between the latter stage SR latch circuit 16 and the other SR latch circuit located in the next segment after the latter stage SR latch circuit 16. The former stage SR latch circuit 12 and the latter stage SR latch circuit 16 are both electrically connected to a forward clock CK and a backward clock XCK. The former stage bidirectional control circuit 14 comprises a forward CMOS 20 and a backward CMOS 22, and the latter stage bidirectional control circuit 18 comprises a forward CMOS 24 and a backward CMOS 26, too. A gate of an N-type MOS in the forward CMOS 20, 24 and a gate of a P-type MOS in the backward CMOS 22, 26 are for receiving a forward control signal FW_control. A gate of a P-type MOS in the forward CMOS 20, 24 and a gate of an N-type MOS in the backward CMOS 22, 26 are for receiving a backward control signal BW_control.
The operation of the bidirectional shift register 10 is as follows. When the forward control signal FW_control has a logic high voltage and the backward control signal BW_control relative to the forward control signal FW_control has a logic low voltage, both the forward CMOS 20 of the former stage bidirectional control circuit 14 and the forward CMOS 24 of the latter stage bidirectional control circuit 18 are electrically on, and both the backward CMOS 22 of the former stage bidirectional control circuit 14 and the backward CMOS 26 of the latter stage bidirectional control circuit 18 are off.
FIG. 2 shows the circuit diagram of the CMOS bidirectional shift register 10 without displaying the off circuits as in FIG. 1 described above. The signal received in a forward input end INPUT_FW of the bidirectional shift register 10 goes to an input end IN of the former stage SR latch circuit 14, to an output end OUT of the former SR latch circuit 12, to the former CMOS 20 of the forward bidirectional control circuit 14, to an input end IN of the latter stage SR latch circuit 16, to an output end OUT of the latter stage SR latch circuit 16, to the forward CMOS 24 of the latter stage bidirectional control circuit 18, and to a forward output end OUTPUT_FW of the bidirectional shift register 10 in order.
On the other hand, when the forward control signal FW_control has a logical low voltage and the backward control signal BW_control has a logical high voltage, both the forward CMOS 20 of the former stage bidirectional control circuit 14 and the forward CMOS 24 of the backward bidirectional control circuit 18 are off, while both the backward CMOS 22 of the former stage bidirectional control circuit 14 and the backward CMOS 26 of the latter stage bidirectional control circuit 18 are on. This is shown in FIG. 3 without displaying the off circuits for clarity. In this case, the signal received in a backward input end INPUT_BW of the bidirectional shift register 10 goes to the backward CMOS 26 of the latter stage control circuit 18, to the input end IN of the latter stage SR latch circuit 16, to the output end OUT of the latter stage latch circuit 16, to the backward CMOS 22 of the former stage bidirectional control circuit 14, to the input end IN of the former stage SR latch circuit 12, to the output end OUT of the former stage SR latch circuit 12, and to a backward output end OUTPUT_BW of the bidirectional shift register 10 in order.
However, since the bidirectional shift register 10 includes CMOS elements, such as the forward CMOS 20 and the backward CMOS 26, two sets of different photo masks are needed when manufacturing the bidirectional shift register 10, therefore increasing the manufacturing cost.